Other underhand methods used by banks to prevent customers pursuing their case include threatening to close accounts, charging for statements and ignoring customer letters, according to Which?
The consumer watchdog also found that some customers have been offered loans or increased overdrafts instead of refunds, thereby increasing the risk of bad debt.
Personal finance campaigner Doug Taylor said: “In an attempt to avoid paying consumers what they are due, we have found that banks are employing increasingly underhand methods to avoid their responsibility to treat their customers fairly and refund the charges.”
He added that that it is vital that the banks’ dirty tricks do not deter people from reclaiming their charges.
Angela Knight, from the British Bankers’ Association, said that although the research could have been useful, Which? has chosen to sensationalise its findings.
“The banking industry handles over seven billion transactions a year and occasionally something will go wrong that’s human nature,” she stated.